Projector and method of controlling a light source for use with the projector

ABSTRACT

A projector has a storage unit storing data on a plurality of different light emission patterns each occurring in a period based on a plurality of different-colored lights, wherein each light emission pattern corresponds to a respective one of a plurality of different projection conditions of a color image. An acquiring unit acquires a present projection condition of the color image, and a controller controls a light emission operation of the plurality of different-colored light emitting elements in the period in accordance with data on a light emission pattern corresponding to the present projection condition of the color image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2005-284561, filed Sep. 29, 2005,the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a projector of a field sequential colortype and a method of controlling a light source for use with theprojector.

2. Description of the Related Art

In the past, in meetings or presentations projectors are used whichconvert an image signal received from an image supply device such as acomputer to projection light, which is then magnified and projected ontoa screen or a white board. Such projectors include the ones of a typecalled a field sequential color type which is capable of projecting acolor image. In a projector of such type, a color wheel of red (R),green (G) and blue (B) filter sections arranged therein in the rotatingdirection thereof is rotated, and light from a light source is caused topass through the R, G and B sections sequentially, thereby producingcorresponding colored light. These light are then caused to enter liquidcrystal or a display device such as a micromirror array, therebydisplaying and projecting a full color image.

Published Unexamined Japanese Patent Application 2004-151650 discloses aprojector which does not produce R, G and B light from a single lightsource, but uses a light source of three different color (R, G and B)LEDs (Light Emitting Diodes) which are switched on sequentially in atime-divisional manner in a period. The Application also discloses thatif the switch-on time of the green LED is set longer than those of thered and blue LEDs and a light flux quantity of the green light is set to60-80 percent of the whole light flux quantity, a white projected imagewill be obtained.

Although this projector can provide a white projected image, theswitch-on time of each color light of the light source is fixed in alight emission period of the light source. Thus, there is naturally alimit to improvement of the quality of the projected images.

BRIEF SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a projectorincluding a light source of a plurality of different-colored lightemitting elements for projecting a color image in a field sequentialcolor system, the projector comprises:

a storage unit which stores data on a plurality of different lightemission patterns each occurring in a period based on a plurality ofdifferent-colored lights emitted by the plurality of different-coloredlight emitting elements, each pattern corresponding to a respective oneof a plurality of different projection conditions of the color image;

an acquiring unit which acquires a present projection condition of thecolor image;

a reader which reads from the storage unit data on a light emissionpattern corresponding to the present projection condition of the colorimage acquired by the acquiring unit; and

a controller which controls a light emission operation of the pluralityof different light emitting elements in a period in accordance with theread data on a light emission pattern.

According to another embodiment of the present invention, in a projectorincluding a light source of a plurality of different-colored lightemitting elements for projecting a color image in a field sequentialcolor system, a method of controlling a light emission operation of theplurality of light emission elements of the light source in a period,the method comprises:

acquiring a present projection condition of the color image;

reading data on a light emission pattern corresponding to the acquiredpresent projection condition from a storage unit which stores data on aplurality of different light emission patterns for a period; and

controlling a light emission operation of the plurality of differentlight emitting elements in a period in accordance with the read data ona light emission pattern.

According to an embodiment of the present invention, a software programproduct embodied in a computer readable medium for performing the abovemethod of controlling a light emission.

The above and other objects, features and advantages of the presentinvention will become apparent in the following detailed description ofthe present embodiment and modifications thereof when read inconjunction with the accompanying drawings wherein the same referencenumerals denote like or similar parts throughout the several views.

Additional objects and advantages of the present invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the present invention.

The objects and advantages of the present invention may be realized andobtained by means of the instrumentalities and combinations particularlypointed out hereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the presentinvention and, together with the general description given above and thedetailed description of the embodiments given below, serve to explainthe principles of the present invention in which:

FIG. 1 is a block diagram of a projector which is used in common in allembodiments of the present invention;

FIG. 2 illustrates the construction of a light source of the projectorof FIG. 1;

FIG. 3 illustrates a light emission pattern corresponding to a luminousintensity level 1 in the first embodiment;

FIG. 4 illustrates a light emission pattern corresponding to a luminousintensity level 2;

FIG. 5 illustrates a light emission pattern corresponding to a luminousintensity level 3;

FIG. 6 is a flowchart indicative of a light source control process to beperformed by a controller of the embodiment;

FIG. 7 illustrates a light emission pattern to be used in amodification;

FIG. 8 illustrates a light emission pattern to be used in anothermodification;

FIG. 9 illustrates a yellow emphasis light emission pattern to be usedin a second embodiment;

FIG. 10 illustrates a complementary color emphasis light emissionpattern to be used in the second embodiment; and

FIG. 11 is a flowchart indicative of a light-source control process tobe performed by the controller in the second embodiment.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of a projector according to the present invention will nowbe described with reference to the accompanying drawings.

First Embodiment

FIG. 1 is a block diagram of a projector which is used in common in twoembodiments of the present invention. Referring to FIG. 1, the projector1 has an input/output connector 2 provided on a body (not shown) andincluding a USB terminal that receives/delivers image data from/to anexternal device such as, for example, a computer, and a mini D-SUBterminal, an S terminal and an RCA terminal for reception of videoimages.

Various standard image signals received through the input/outputconnector 2 are standardized to image signals of a predetermined formatby an image converter 4 through an input/output interface (I/F) 3 and asystem bus SB and then forwarded to a projection encoder 5. The encoder5 loads and stores a respective received image signal on and in a videoRAM 6. The encoder 5 also produces a video signal based on the imagesignal stored in the video RAM 6 and forwards it to a projection driver7.

The projection driver 7 drives a spatial light modulator (SLM) 8 fordisplaying purposes at a predetermined frame rate, for example of 30frames/second, based on the received image signal. When light emitted bya light source 9, which will be described in detail later, is applied tothe spatial light modulator 8, an optical image is formed by areflection from the modulator 8 and projected onto a screen (not shown)via a projection lens unit 10. The projection lens unit 10, which iscomposed of lenses, and has zoom and focus functions, is driven by alens motor 11 so as to adjust the zoom and focus positions as required.

FIG. 2 shows the construction of the light source 9, which includes adichroic mirror 91 and LEDs 90R, 90G and 90B that emit red, green andblue lights, respectively, arranged around the dichroic mirror 91. Lightfluxes from the LEDs 90R, 90G and 90B are focused individually by acondenser lens 92 on the dichroic mirror 91, in which the focused lightfluxes are then combined. These combined light fluxes are then guidedinto and reflected repeatedly within a light tunnel 93, therebyproviding an equalized light flux. This flux is then projected through alight source lens 94 against the spatial optical modulator 8.

The components of the projector 1 are controlled by the controller 12,which mainly includes a CPU, a ROM 12 a that permanently stores anoperation program to be executed by the CPU, and a RAM to be used as aworking memory.

The controller 12 is connected to the input/output interface 3, theimage converter 4, the projection encoder 5, a display driver 13, and aluminous intensity detector 15 through the system bus SB. The displaydriver 13 drives a display unit 14 composed of a liquid crystal panel inaccordance with commands from the controller 12, thereby causing thedisplay unit 14 to display an operative state of the projector 1 andvarious guide messages. The luminous intensity detector 15 includes anoptical sensor such as a photoresistor or a photocell, and an amplifierand forwards a detection signal indicative of a luminous intensity ofthe projector's environment to the controller 12.

The controller 12 is connected to a key input unit 16 that comprisesvarious operation buttons (not shown) including a power source button.When any one of the operation buttons is operated, the key input unit 16delivers a corresponding operation signal to the controller 12.

The ROM 12 a of the controller 12 has stored data indicative ofinventive light emission patterns for the LEDs 90R, 90G and 90B of thelight source 9 in a single period corresponding to predeterminedluminous intensities and used for controlling purposes later, which willbe described later in detail. In the present embodiment, the number ofpredetermined luminous intensity levels is three and the respectiveluminous intensity levels are determined depending on an emissionperformance of projection light of the light source 9; that is, a level1 that represents a luminous intensity in a range suitable forprojection of an image, a level 2 that represents a luminous intensityin a range somewhat higher than at the level 1, and a level 3 thatrepresents a luminous intensity in a range higher than at the level 2.

Light emission patterns corresponding to the respective luminousintensity levels are determined as follows. FIGS. 3-5 show lightemission patterns corresponding to the luminous intensity levels 1-3,respectively.

As shown in FIG. 3, the light emission pattern corresponding to theluminous intensity level 1 includes only successive light emissiondurations α for which the LEDs 90R (or R-LED), 90G (or G-LED) and 90B(or B-LED) are sequentially switched on, thereby causing the lightsource 9 to emit R (red), G (green) and B (blue) lights in atime-divisional manner.

As shown in FIG. 4, the light emission pattern corresponding to theluminous intensity level 2 includes successive light emission durationsa for which the LEDs 90R (or R-LED), 90G (or G-LED) and 90B (or B-LED)are sequentially switched on, and then the last light emission durationβ for which the LEDs 90R (or R-LED), 90G (or G-LED) and 90B (or B-LED)are simultaneously switched on, thereby causing the light source 9 toemit R, G, B and W (white) lights sequentially in a time-divisionalmanner. The percentage of the W light duration in a single period is25%.

As shown in FIG. 5, like the light emission pattern of the luminousintensity level 2 the light emission pattern corresponding to theluminous intensity level 3 includes successive light emission durationsα for which the LEDs 90R (or R-LED), 90G (or G-LED) and 90B (or B-LED)are sequentially switched on, and then the last light emission durationβ for which the LEDs 90R (or R-LED), 90G (or G-LED) and 90B (or B-LED)are simultaneously switched on, thereby causing the light source 9 toemit R, G, B and W (white) lights sequentially in a time-divisionalmanner. The percentage of each of the R, G and B light durations α in asingle period is 16.6(=⅙×100)%, and the percentage of the W lightduration in the single period is 50%.

Operation of the inventive projector 1 will be described next. FIG. 6 isa flowchart indicative of a light-source control process to be executedby the controller 12 when or after a user turns on the power sourceswitch and then performs a predetermined operation. Herein, it isassumed that image data received, for example, from a personal computerinvolves a color image.

The controller 12 starts to operate in accordance with the turning on ofthe power source. First, the controller 12 acquires data on the luminousintensity of the projector's environment based on a detection signalfrom the luminous intensity detector 15 (step SA1). The controller 12then determines to which of the luminous intensity levels the acquiredluminous intensity corresponds (step SA2), and reads out correspondinglight emission pattern data from the ROM 12 a (step SA3). The controller12 then starts switch-on control of the LEDs 90R, 90G and 90B of thelight source 9 and drive control of the spatial light modulator 8 in asynchronous manner (step SA4) and then terminates this process.

Thus, if the luminous intensity of the projector's environment is underthe projection conditions at the luminous intensity level 1 when thepower source is turned on, an image similar to a conventional one isprojected in three primary R, G and B lights. If the luminous intensityof the projector's environment is under the projection conditions at theluminous intensity level 2 or 3, an image is projected in three primaryR, G and B lights and W light. Thus, a high-luminosity image of somewhatreduced saturation is projected. As the luminous intensity of theprojector's environment is higher, the luminosity of the projected imageis higher.

Thus, when the place where the image projection is performed is at aluminous intensity suitable for image projection (or dark), thepercentage of the W light emission duration in a period is zeroed,thereby obtaining a projected image of usual saturation. When the placewhere the image projection is performed is relatively bright, thepercentage of the W light emission duration, or the luminosity, isincreased, which provides a plain projected image, thereby restricting areduction in the contrast of the image due to external light. That is, alight emission pattern suitable for the luminous intensity of the imageprojection environment is obtained automatically in a switched mannerand hence an improved quality image is projected.

While in the embodiment the luminous intensities of the projector'senvironment are illustrated as separated into three levels and hence thepercentages of W light durations in the period of the light sourceoperation are illustrated as adjusted automatically to 0, 25 and 50%,respectively, they may be adjusted automatically to finer numericalvalues. While the luminous intensity of the projector's environment isillustrated as detected and acquired as the luminous intensity of theprojection environment, the luminous intensities of an object of imageprojection such as a screen or a white board before and after anyparticular image is projected onto the object of image projection may bedetected, and the luminous intensity of the projector's environment maybe determined or acquired based on a difference between the detectedluminous intensities.

While in the embodiment a light emission pattern is illustrated in whichthe LEDs 90R (or R-LED), 90G (or G-LED) and 90B (B-LED) are onceswitched on sequentially in corresponding durations in a period in orderto emit light including W (white) light from the light source, adifferent light emission pattern such as shown next may be employed.

FIG. 7 is a modification of the present embodiment indicative of a lightemission pattern in which R, W, G, W, B and W light are emittedsequentially in successive durations α, β, α, β, α and β of a period. Inthis case, the percentage of the sum of simultaneous light emissiondurations β in a period may be changed or adjusted depending on theluminous intensity of the projector's environment, thereby producingadvantageous effects similar to those of the embodiment. Distribution ofthe simultaneous light emission durations β serves to reduce flickeringof the projected image due to an increase in the luminosity of theimage, and also reduce the respective light emission durations of theLEDs 90R, 90G and 90B, thereby restricting a rise in their temperature(due to their heat generation).

While the above description illustrates that the light emission patternsof the LEDs 90R, 90G and 90B of the light source 9 include durations forwhich the W light is emitted, the ROM 12 a may store data indicative ofa light emission pattern in which the light source emits no W light,which will be described next.

FIG. 8 shows another modification in which light emission pattern theLEDs 90R, 90G and 90B are once switched on sequentially at a fullluminosity for their durations γ in this order in a period and the othertwo LEDs (for example, 90G and 90B) excluding the particular LED (forexample, 90R) that emits corresponding colored light at the fullluminosity emit corresponding colored light at a predeterminedluminosity lower than the full luminosity, which is hereinafter referredto as an auxiliary light luminosity, for the duration for which theparticular LED emits its light. Light emission patterns different onlyin auxiliary light luminosity from FIG. 8 modification pattern may bestored in correspondence with different luminous intensity levels in theROM 12 a. A higher auxiliary light luminosity is set in a light emissionpattern corresponding to a higher luminous intensity. A zero auxiliarylight luminosity is set in a light emission pattern corresponding to thelowest luminous intensity at level 1, or the other two LEDs excludingthe particular LED that emits corresponding colored light at the maximumluminosity may be switched off. It is noted that the luminosity of eachLED will be determined depending on a current flowing through that LEDand that the spatial light modulator 8 will be driven irrespective ofthe luminous intensity of the projector's environment.

When the place where the image projection is performed is relativelybright, the auxiliary light luminosity is increased depending on theluminous intensity of the environment of the object of image projection,thereby projecting a high luminous-intensity image of somewhat reducedreproducibility of colors. As the environment of the projector and hencethe place where the image projection is performed are brighter, theluminosity of the projected image is higher. Thus, a plain projectedimage is obtained in which a reduction in the contrast thereof due toexternal light is restricted.

Second Embodiment

In a second embodiment, the ROM 12 a of the projector's controller 12stores data on a light emission pattern similar to that of FIG. 3 in thefirst embodiment (hereinafter referred to as a usual light emissionpattern), a yellow emphasis light emission pattern of FIG. 9, and acomplementary color emphasis light emission pattern of FIG. 10 as thelight emission patterns of the LEDs 90R, 90G and 90B for a period.

As shown in FIG. 9, in the yellow emphasis light emission pattern theR-LED; the two R- and G-LEDs; the G-LED; the B-LED; and the three R-, G-and B-LEDs are switched on sequentially for successive durations α, δ,α, α, and β of a period, thereby emitting R, Y, G, B and W lightsequentially in a time-divisional manner. The duration times β and δ areequal and shorter than the duration α.

As shown in FIG. 10, in the complementary-color emphasis light emissionpattern the R-LED; the two R- and G-LEDs; the three R-, G- and B-LEDs;the G-LED; the two G- and B-LEDs; the three R-, G- and B-LEDs; theB-LED; the two R- and B-LEDs; and the three R-, G- and B-LEDs areswitched on sequentially for successive durations α, δ, β, α, ε, β, α, ζand β of a period, thereby emitting R, Y, W, G, C (Cyan), W, B, M(Magenta) and W light sequentially in a time-divisional manner. Thedurations δ, β, ε, and ζ are equal and shorter than the duration α.

Next, operation of the projector in the second embodiment will bedescribed. FIG. 11 is a flowchart indicative of a light source controlprocess to be performed by the controller 12 while a color image basedon image data received, for example, from a personal computer is beingprojected onto a screen.

The controller 12 starts the processing along with the beginning of theimage projection. The controller 12 first confirms colors contained inthe received image (to be projected) (step SB1). If the image containsno complementary colors (No in step SB1), the controller 12 reads dataon the usual light emission pattern from the ROM 12 a (step SB3), andthen starts switch-on control of the LEDs 90R, 90G and 90B of the lightsource 9 in accordance with the usual light emission pattern and drivecontrol of the spatial light modulator 8 in a synchronous manner (stepSB7), thereby projecting an image similar to a conventional image inthree primary color or R, G and B light.

When the received image contains complementary colors, which are onlyyellow (steps SB2 and SB4), the controller 12 reads data on the yellowemphasis light emission pattern from the ROM 12 a (step SB5), and thenstarts light emission control of the LEDs 90R, 90G and 90B of the lightsource 9 in accordance with the yellow emphasis light emission patternand drive control of the spatial light modulator 8 in a synchronousmanner (step SB7).

Since in this case the light source 9 emits light including Y light, aprojected image is obtained whose yellow part is improved in colorreproducibility. In addition, since the light emitted by the lightsource 9 includes W light at the same percentage in duration as the Ylight, the luminous intensity of the projected image is not lowered, butthe color reproducibility of a yellow part of the image is improved.

When the received image contains a plurality of different complementarycolors including yellow or otherwise a plurality of differentcomplementary colors other than yellow (YES in step SB2, NO in stepSB4), the controller 12 reads data on the complementary color emphasislight emission pattern from the ROM 12 a (step SB6), and then startslight emission control of the LEDs 90R, 90G and 90B of the light source9 in accordance with the read complementary color emphasis lightemission pattern and drive control of the spatial light modulator 8 in asynchronous manner (step SB7).

Since in this case the light emitted by the light source 9 includes Y, Cand M light complementary to R, G and B light, a projected image isobtained which is improved in the color reproducibility of thecomplementary parts thereof. In addition, since the light emitted by thelight source 9 contains W light at the same percentage in duration aseach of the plurality of complementary colors, the whole luminousintensity of the projected image is not lowered, but the colorreproducibility of the complementary color parts of the image isimproved. In addition, since the simultaneous light emission durations βfor which the W light is emitted from the light source 9 are distributedin the respective durations α, flickering of the image which wouldotherwise occur is reduced. Furthermore, since the duration time forwhich each of the LEDs 90R, 90G and 90B emits corresponding light isshort and hence a rise in the temperature of these LEDs due to theirgenerated heat is restricted.

After starting the light emission control of the LEDs 90R, 90G and 90Bof the light source 9 in accordance with any particular one of the lightemission patterns mentioned above and drive control of the spatialoptical modulator 8, the controller 12 returns to step SB1, therebyrepeating the process of FIG. 11 each time a different image is received(YES in step SB8).

As described above, in the present embodiment the light emission patternof the LEDs 90R, 90G and 90B of the light source 9 can be changedautomatically in a switched manner to a light emission pattern suitablefor the composition of colors contained in a received image to beprojected. Thus, an improved quality image can be projected onto ascreen or the like.

While in the present embodiment the yellow emphasis light emissionpattern (see FIG. 9) and the complementary color emphasis light emissionpattern (see FIG. 10) are illustrated as including a simultaneous lightemission duration β for which the W light is emitted from the lightsource 9, thereby preventing the luminous intensity of a projected imagefrom being lowered, the color reproducibility of a yellow or acomplementary color part of the image can be improved even when thesimultaneous light emission durations are eliminated.

Although not shown, the ROM 12 a may store data indicative of aplurality of different usual light emission patterns each including adifferent simultaneous light emission duration β in a period, similar tothose of FIGS. 4 and 5 of the first embodiment, a plurality of differentyellow emphasis light emission patterns each including a differentsimultaneous light emission duration (percentage) β in a period, and aplurality of different complementary-color emphasis light emissionpatterns in correspondence with a like number of luminous intensitylevels such that the controller 12 reads from the ROM 12 a a lightemission pattern corresponding to a level of the luminous intensity ofthe projector's environment detected and stored when the power source isturned on at steps SB3, SB5 and SB6. In this case, since the lightemission pattern of the LEDs 90R, 90G and 90B of the light source 9 canbe switched automatically to a light emission pattern suitable for boththe composition of colors contained in the received image (to beprojected) and the luminous intensity of the projector's environment, animproved quality image can be projected.

The present invention has been described with reference to severalexemplary embodiments and modifications. However, it will be readilyapparent to those skilled in the art that it is possible to embody theinvention in specific forms other than those of the exemplaryembodiments and modifications described above. This may be done withoutdeparting from the spirit of the invention. These exemplary embodimentsand modifications are merely illustrative and should not be consideredrestrictive in any way. The scope of the invention is given by theappended claims, rather than the preceding description, and allvariations and equivalents which fall within the range of the claims areintended to be embraced therein.

1. A projector including a light source of a plurality ofdifferent-colored light emitting elements and a display element forreceiving an image signal, the projector projecting a color image in afield sequential color system, the projector comprising: a storage unitwhich stores data on a plurality of different light emission patternseach occurring in a period based on a plurality of different-coloredlights emitted by the plurality of different-colored light emittingelements, wherein each light emission pattern corresponds to arespective one of a plurality of different projection conditions of thecolor image; an acquiring unit which acquires a present projectioncondition of the color image; a reader which reads from the storage unitdata on a light emission pattern corresponding to the present projectioncondition of the color image acquired by the acquiring unit; and acontroller which controls a light emission operation of the plurality ofdifferent-colored light emitting elements in the period in accordancewith the read data on a light emission pattern; wherein the presentprojection condition of the image acquired by the acquiring unitcomprises a luminous intensity of a projection environment of the colorimage; wherein the plurality of different-colored light emittingelements respectively emit red, green and blue light; wherein theplurality of light emission patterns whose data are stored in thestorage unit cause the plurality of different-colored light emittingelements to respectively emit one of red, green and blue lightssequentially in successive durations at a full brightness and, in eachrespective successive duration, cause the other light emitting elementswhich are not emitting their respective corresponding colored light atthe full brightness in that particular duration to respectively emittheir corresponding colored light simultaneously for that particularduration at a predetermined brightness lower than the full brightness;wherein during a given one of the durations, an image signalcorresponding to the one of the red, green and blue lights which isemitted at the full brightness is supplied to the display element; andwherein the brightness that is lower than the full brightness at whichthe other light emitting elements are caused to respectively emit theircorresponding colored light simultaneously for that duration isdifferent for each of the plurality of light emission patterns.
 2. Theprojector of claim 1, wherein the storage unit stores data on anotherplurality of different light emission patterns which are different in alength of a duration in a period in which white light is emitted.
 3. Theprojector of claim 2, wherein each of the another plurality of lightemission patterns comprises successive individual light emissiondurations in which the different-colored light emitting elementsrespectively emit red, green and blue light sequentially andindependently, and a simultaneous light emission duration in which thedifferent-colored light emitting elements respectively emit red, greenand blue light simultaneously so as to provide white light.
 4. Theprojector of claim 3, wherein the simultaneous light emission durationis between each of the individual light emission durations in arespective one of the another plurality of light emission patterns. 5.The projector of claim 1, wherein the present projection conditionacquired by the acquiring unit further comprises a composition of colorsof the color image.
 6. The projector of claim 5, wherein the storageunit stores data on a further plurality of light emission patterns whichcomprise a pattern that corresponds to a case in which the compositionof colors of the color image acquired by the acquiring unit includesyellow, and said pattern includes a duration in which only the lightemitting elements that respectively emit red and green light emit theircorresponding colored light simultaneously.
 7. The projector of claim 5,wherein the storage unit stores data on a further plurality of lightemission patterns which comprise a pattern that corresponds to a case inwhich the composition of colors of the color image acquired by theacquiring unit includes a complementary color, and said pattern includesa first simultaneous light emission duration in which only the lightemitting elements that respectively emit red and green light emit theircorresponding colored light simultaneously, a second simultaneous lightemission duration in which only the light emitting elements thatrespectively emit green and blue light emit their corresponding coloredlight simultaneously, and a third simultaneous light emission durationin which only the light emitting elements that respectively emit red andblue light emit their corresponding colored light simultaneously.
 8. Theprojector of claim 6, wherein the pattern that corresponds to the casefurther comprises a simultaneous light emission duration in which all ofthe plurality of light emitting elements emit their correspondingcolored light simultaneously.
 9. A control method for a projectorincluding a light source of a plurality of different-colored lightemitting elements and a display element for receiving an image signal,the projector projecting a color image in a field sequential colorsystem, said method controlling a light emission operation of theplurality of light emitting elements of the light source in a period,the method comprising: acquiring a present projection condition of thecolor image; reading data on a light emission pattern corresponding tothe acquired present projection condition from a storage unit whichstores data on a plurality of different light emission patterns for theperiod; and controlling a light emission operation of the plurality ofdifferent-colored light emitting elements in the period in accordancewith the read data on a light emission pattern, wherein the acquiredpresent projection condition of the image comprises a luminous intensityof a projection environment of the color image; wherein the plurality ofdifferent-colored light emitting elements respectively emit red, greenand blue light; wherein the plurality of light emission patterns whosedata are stored in the storage unit cause the plurality ofdifferent-colored light emitting elements to respectively emit one ofred, green and blue lights sequentially in successive durations at afull brightness and, in each respective successive duration, cause theother light emitting elements which are not emitting their respectivecorresponding colored light at the full brightness in that particularduration to respectively emit their corresponding colored lightsimultaneously for that particular duration at a predeterminedbrightness lower than the full brightness; wherein during a given one ofthe durations, an image signal corresponding to the one of the red,green and blue lights which is emitted at the full brightness issupplied to the display element; and wherein the brightness that islower than the full brightness at which the other light emittingelements are caused to respectively emit their corresponding coloredlight simultaneously for that duration is different for each of theplurality of light emission patterns.
 10. A non-transitorycomputer-readable medium having stored thereon a program that isexecutable by a computer to perform the method of claim
 9. 11. Aprojector which projects a color image in a field sequential colorsystem, the projector comprising: a light source comprising lightemitting elements of three colors; a display element configured toreceive an image signal; a controller configured to control the lightsource to respectively emit light of one of the three colorssequentially in successive durations at full brightness and, in eachrespective successive duration, to emit light of the other two of thethree colors at a predetermined brightness lower than the fullbrightness; wherein during a given one of the durations, an image signalof the one of the three colors which is emitted at the full brightnessis supplied to the display element.
 12. The projector according to claim11, further comprising an acquiring unit configured to acquire a presentprojection condition of the color image, wherein the controller isconfigured to control the light source based on the acquired presentprojection condition of the color image.
 13. The projector according toclaim 11, further comprising a storage unit configured to store data ona plurality of different light emission patterns, wherein the controlleris configured to control the light source based on the light emissionpatterns.